Why is scanned image all 'dotty'?

I originally had a older Lexmark scanner and when a printed color image is scanned at 300 DPI, it would come up as more sharp and the halftone like dots would be dark and blend in. I recently got a newer HP Photosmart 2575 scanner and now the scans come up with the halftone dots all bright, and white. I have tested it and its only on this scanner not the old one. Anyone one know what could cause this or if its a setting problem?